[Venous valves in the legs: hemodynamic and biological problems and relationship to physiopathology].
Venous valves are more frequent in distal veins and venulae, providing a protecting action against blood skin reflux. Structurally simple, collagen and endothelium, they allow a cavity to be formed by distension, when occlusion occurs. Venous angioscopy can distinguish bicuspid floating valves, reinforced, reinforcing valves with free edges and seat valves as well as the presence of apertures of small collateral vessels in the sinus, of which they play a role in the filling up. Valves are inefficient in supine and in standing among 20% of the adult population. Sinuses allow vortices to be created, low recirculating zones, where blood flow move slowly in niches, at a low shear rate, independently from the main stream. A deep vortex is located in sinus, usually empty, but likely to receive red cell aggregates and leukocytes in the condition of stasis and hyperviscosity. Such a vortex is hypoxic, cause of endothelial activation. In such areas fibrin-leucocytic nidus are created, histologically recognized, of which sub-endothelium has become thick and thrombogenic. Two stages characterized its progression: stage I: a few alteration in the valves, little thrombin generation, taken over by the coagulation inhibitors: AT III, APC and TFPI. Stage II: damaged valves, local consumption of the inhibitors and extended generation of thrombin over the platelets, through factor IXa. Hereditary inhibitor deficits increase the risk (frequent factor Leyden V). When the coagulation cascade is considered, VIIa-tissue factor complex appears to be the thrombotic pathway, leading first to wall linked thrombin, uneasily reached by AT III and facteur IXa non inhibited by TFPI, therefore explaining the platelet extension. Monocytes, which can bear tissue factor, may be "lodged" inside the niches. Besides this important role in deep venous thrombosis, incompetent venous valves are responsible for the skin venous hypertension, a subsequent ground for ulcers. Their role in chronic venous insufficiency is uncertain. In the near future, venous angioscopy will bring about new findings about the pathophysiology of venous valves.
Boisseau
M R
MR
Laboratoire d'hématologie, Université Victor-Segalen Bordeaux II.
D005337:Fibrin / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D007866:Leg / Q000098:blood supply*; D007962:Leukocytes / Q000502:physiology; D013924:Thrombophlebitis / Q000503:physiopathology; D014680:Veins / Q000503:physiopathology*
D005337:Fibrin
Valvules veineuses des membres inférieurs: problèmes hémodynamiques, biologiques et relations physiopathologiques.